Dynamic stair walking of biped humanoid robots

Biped humanoid robots are expected to move around human-centered setting that includes stairs as a major terrain. Reportedly, however, only few of them can walk up and down stairways as of now. Making it worse, even the successful ones carry out such motions either barely in terms of speed or fast enough but in an undisclosed technical manner. In this context, a dynamic gait pattern is proposed anew suitable for stair walks along with a transient pattern and verified by means of a multi-body dynamics analysis software.     

Optimal trajectory planning with application to industrial robots

A procedure is presented for planning optimal trajectories for application to industrial robots. First, trajectories are optimised by considering the nominal dynamics of a robot with rigid links and joints and with constraints on joint torque and speed. The minimum-time optimisation criterion is complemented by a miminal dynamic energy criterion that leads to smoother actuator inputs that do not excite joint vibrations. Weighting factors for these cost functions are then determined by trial simulations. By these means the effect of controller characteristics and elasticity, friction and backlash in the joints may be taken into account. A minimum-time movement for the real-world robot is obtained which displays the dynamical behaviour predicted in the planning procedure. Results from measurements and simulations for a PUMA 562 robot illustrate the approach. Further improvements may be achieved by a custom controller with the feedforward torques as shown in a comparison of trajectories executed with a VAL2 controller and a custom controller.     

Trajectory generation and dynamic control of planar biped robots with curved soles

This paper proposes a locomotion pattern and a control method for biped robots with curved soles. First, since the contact point of a supporting leg may arbitrarily move back and forth on the ground, we derived the desired trajectory from a model called the Moving Inverted Pendulum Model (MIPM) where the Zero Moment Point (ZMP) exists at the supporting point and can be moved intentionally. Secondly, a biped robot with curved soles is an under-actuated system since the supporting point contacting with a point on the ground has no actuator during the single supporting phase. Therefore, this paper proposes a computed-torque control for this under-actuated system using decoupled dynamic equations. A series of computer simulations with a 7-DOF biped robot with curved soles shows that the proposed walking pattern and control method are effective and allow the biped robot to walk fast and stably, and move more like human beings. Also, it is shown that the curved sole shape has superior energy consumption compared to flat soles, and greater efficiency in ascending and descending the stairs.     

基于人工生命算法的并联机器人最优轨迹规划

基于机器人直纹面概念和人工生命算法,提出一种并联机器人位姿轨迹最优规划方法.应用计算几何中的三维直纹面生成原理,对机器人末端执行器的位置和姿态进行统一描述.考虑到机器人姿态直纹面面积及其变化率能够反映和评价机器人的运动学和动力学性能,通过求解等效角位移矢量在空间的运动轨迹形成的三维直纹曲面面积及其变化率,并将其作为泛函的泛函极值,同时考虑运动时机器人的灵活度,建立机器人位置和姿态轨迹优化的数学模型.采用人工生命优化算法对代表并联机器人位姿轨迹的高阶参数化空间曲线的参数进行优选,通过优化轨迹直纹曲面面积及其变化率和机器人的灵巧度,使并联机器人具有良好的运动学和动力学性能.最后以一三自由度球面并联机器人轨迹规划实例,验证所提出方法的可行性.     

Energy efficient walking control for biped robots using interval type-2 fuzzy logic systems and optimized iteration algorithm

An energy efficient approach is proposed for the walking control of bipedal robots. To compensate the ZMP error caused by model uncertainties and external disturbances, we design a new walking controller in this paper. Different from currently available control schemes for cancelling ZMP error, our newly proposed one additionally incorporates a fuzzy logic systems(FLSs) mechanism and an iterative mechanism. By employing FLSs to deduce Center of Mass(CoM) correction according to ZMP error and designing iterative mechanism to compute the optimal joint position, the newly proposed controller exhibits an excellent performance. To tackle the control difficulties arising from physical constraints of actuators and hard-to-stabilization of biped robot, an optimized control algorithm is included in the iterative mechanism to guarantee the convergence to the optimal solution. Moreover, the interval type-2 FLSs are adopted to handle the uncertainties. Finally, the experiment results are provided to validate the proposed control scheme.     

Accuracy analysis of optimal trajectory planning methods based,on function approximation for a four-DOF biped walking model

Based on an introduced optimal trajectory planning method, this paper mainly deals with the accuracy analysis during the function approximation process of the optimal trajectory planning method The basis functions are composed of Hermit polynomials and Founer series to improve the approximation accuracy Since the approximation accuracy is affected by the given orders of each basis function, the accuracy of the optimal solution is examined by changing the combinations of the orders of Hermit polynomials and Fourier series as the approximation basis functions As a result, it is found that the proper approximation basis functions are the 5^th order Hermit polynomials and the 7^th-10^th order of Fourier series

     

基于小驱动力矩函数驱动的多足步行机器人轨迹规划问题研究

在研究轨迹规划中,用小驱动力矩函数控制机器人的质心运动,降低机器人关节的驱动电机的功率问题。文中首先对相关理论进行了描述,根据多足步行机器人的运动关系导出机器人的质心运动规律与关节驱动变化在能耗上的联系,并利用泛函理论导出小驱动力矩函数。在机器人ZQROT-I运行直线步态过程中,采用该函数控制机器人质心的运动,利用ADAMS对机器人的运动性能进行了分析,并将结果与机器人轨迹控制中采用其他函数的运行结果进行了对比分析。结果表明,采用小驱动力矩函数控制机器人的质心轨迹运动,在节省机器人运行能耗方面有一定的作用。     

Design of a robust self-excited biped walking mechanism

A self-excited biped walking mechanism consisting of two legs that are connected in a series at the hip joint through a servomotor is studied to determine range of stability. A torque proportional to angle between the shank and the vertical is seen to sustain a gait. Each leg has a thigh and a shank connected at a passive knee joint that has a knee stopper restricting the forward motion like the human knee. While a torque proportional to the angle between the shank and the vertical stabilises, the optimum proportionality constant is to be determined. A mathematical model for the dynamics of the system including the impact equations is used to analyze the stability of the system through examination of phase plane plots. For a specified proportionality constant, the range of physical parameters like leg-length and mass of leg for which the system is stable is determined. Using the stability data, a robust design has been made.     

双足机器人稳定步行模式的预测控制实现方法

在双足机器人上应用预测控制设计了具有一个关键参数的步态生成方法,预测控制是通过控制质心运动生成步行模式的。根据预测控制器模型研究了参数间的关系,最终将独立参数减少到一个并讨论了取值范围。关键参数具有明确的物理意义,在容许取值范围内,可以保证系统的稳定性并生成满足稳定步行的质心运动。实验验证了在存在扰动情况下,关键参数的适当值能够生成稳定的步行模式,同时实验结论为预测控制器的参数调控提供了参考。     

Evolutionary collision-free optimal trajectory planning for intelligent robots

This paper presents optimization procedures based on evolutionary algorithms such as the elitist non-dominated sorting genetic algorithm (NSGA-II) and differential evolution (DE) for solving the trajectory planning problem of intelligent robot manipulators with the prevalence of fixed, moving, and oscillating obstacles. The aim is the minimization of a combined objective function, with the constraints being actuator constraints, joint limits, and the obstacle avoidance constraint by considering dynamic equations of motion. Trajectories are defined by B-spline functions. This is a non-linear constrained optimization problem with six objective functions, 31 constraints, and 42 variables. The combined objective function is a weighted balance of transfer time, the mean average of actuator efforts and power, penalty for collision-free motion, singularity avoidance, joint jerks, and joint accelerations. The obstacles are present in the workspace of the robot. The distance between potentially colliding parts is expressed as obstacle avoidance. Further, the motion is represented using translational and rotational matrices. The proposed optimization techniques are explained by applying them to an industrial robot (PUMA 560 robot). Also, the results obtained from NSGA-II and DE are compared and analyzed. This is the first research work which considers all the decision criteria for the trajectory planning of industrial robots with obstacle avoidance. A comprehensive user-friendly general-purpose software package has been developed using VC++ to obtain the optimal solutions using the proposed DE algorithm.     

Footholds optimization for legged robots walking on complex terrain

This paper proposes a novel continuous footholds optimization method for legged robots to expand their walking ability on complex terrains. The algorithm can efficiently run onboard and online by using terrain perception information to protect the robot against slipping or tripping on the edge of obstacles, and to improve its stability and safety when walking on complex terrain. By relying on the depth camera installed on the robot and obtaining the terrain heightmap, the algorithm converts the discrete grid heightmap into a continuous costmap. Then, it constructs an optimization function combined with the robot’s state information to select the next footholds and generate the motion trajectory to control the robot’s locomotion. Compared with most existing footholds selection algorithms that rely on discrete enumeration search, as far as we know, the proposed algorithm is the first to use a continuous optimization method. We successfully implemented the algorithm on a hexapod robot, and verified its feasibility in a walking experiment on a complex terrain.     

Ellipse-based leg-trajectory generation for galloping quadruped robots

Controlling the motions of the front and rear legs and regulating the compliance of the legs are important for stable gallop. In this paper, a new method called ellipse-based trajectory generation method (ETGM) to generate foot trajectories for galloping quadrupeds is proposed. Unlike many previous works which attempted controlling foot trajectory, which need a sophisticated algorithm to avoid forcing the feet out of the workspace and thus making galloping unstable, a new trajectory generation method is based on an elliptic trajectory with constant radii but with changes in its center position. The rotational speed of the elliptic trajectory or the orbit trajectory is determined by the desired height of galloping and the running speed. It is assumed that each leg of a galloping quadruped robot has passive ankle joints with passive springs, thus acting as a spring loaded inverted pendulum (SLIP). To check the performance and effectiveness of the proposed method, a series of computer simulations of a 2-D quadruped robot galloping in the sagittal plane were performed. The simulation results show that the proposed method is simple to implement and very effective in generating stable gallop. This paper was recommended for publication in revised form by Associate Editor Doo Yong Lee Jong Hyeon Park received his B.S. degree in mechanical engineering from Seoul National University in 1981 and his M.S. and Ph.D. degrees from the Massachusetts Institute of Technology in 1983 and 1991, respectively. Since 1992, he has been with the School of Mechanical Engineering at Hanyang University. He was a KOSEF-JSPS Visiting Researcher with Waseda University, Tokyo, Japan, in 1999, and a KOSEFCNR Visiting Researcher with Scuola Superiore Sant’Anna, Pisa, Italy in 2000, a Visiting scholar with MIT, Cambridge, USA, in 2002–2003. He was also associated with Brooks Automation Inc., Chelmsford, MA, in 1991–1992 and 2001–2002.     

工业机器人抓取作业轨迹规划研究

针对8号电雷管的包装生产方式,设计了一种雷管抓取机构,根据工业机器人抓取雷管装盒及抓取雷管盒装箱的运动路径,对机器人进行关节空间轨迹规划。采用5次B样条曲线轨迹规划法,能够实现机器人运动角加加速度的连续性,减少运动产生的冲击及颤振,保证雷管安全、可靠的抓取。最后仿真分析结果证明了该轨迹规划方法的有效性与合理性。     

Employing variable impedance (stiffness/damping) hybrid actuators on lower limb exoskeleton robots for stable and safe walking trajectory tracking

Journal of Mechanical Science and Technology - Compliant actuators are employed in exoskeleton robots instead of stiff actuators for safe human-robot interaction. In parallel with this idea, we...     

教学型双足步行机器人直线行走步态稳定规划方法

通过对双足机器人行走步态的研究,利用多项式插值法对双足机器人直线行走步态进行规划,分析了踝关节轨迹和髋关节轨迹,通过调节单腿支撑期和双腿支撑期的比例系数来调整机器人的行走步态,使其实现稳定步行。再通过ADAMS建立虚拟样机仿真实验,验证了这种步态规划方法的正确性与可行性。     

基于曲柄摇杆机构的新型六足爬行机器人的设计

六足爬行机器人在理论上可以实现向前向后稳定行走.对驱动足采用了曲柄摇杆机构,将腿放在四杆机构的摇杆上,实现了腿前后摇摆行走.此外,由于是通过连杆曲线图谱选择腿部运动轨迹,从连杆曲线图谱上可以看到,整条曲线都是很平滑的,因此,机器人在行走过程中也会非常稳定,而不至于出现冲击载荷.对六足机器人的行进机构、运动设计与分析、机器人的运动轨迹和六足机器人的控制系统进行了详细阐述.     

Motion error compensation of multi-legged walking robots

Existing errors in the structure and kinematic parameters of multi-legged walking robots,the motion trajectory of robot will diverge from the ideal sports requirements in movement.Since the existing error compensation is usually used for control compensation of manipulator arm,the error compensation of multi-legged robots has seldom been explored.In order to reduce the kinematic error of robots,a motion error compensation method based on the feedforward for multi-legged mobile robots is proposed to improve motion precision of a mobile robot.The locus error of a robot body is measured,when robot moves along a given track.Error of driven joint variables is obtained by error calculation model in terms of the locus error of robot body.Error value is used to compensate driven joint variables and modify control model of robot,which can drive the robots following control model modified.The model of the relation between robot’s locus errors and kinematic variables errors is set up to achieve the kinematic error compensation.On the basis of the inverse kinematics of a multi-legged walking robot,the relation between error of the motion trajectory and driven joint variables of robots is discussed.Moreover,the equation set is obtained,which expresses relation among error of driven joint variables,structure parameters and error of robot’s locus.Take MiniQuad as an example,when the robot MiniQuad moves following beeline tread,motion error compensation is studied.The actual locus errors of the robot body are measured before and after compensation in the test.According to the test,variations of the actual coordinate value of the robot centroid in x-direction and z-direction are reduced more than one time.The kinematic errors of robot body are reduced effectively by the use of the motion error compensation method based on the feedforward.     

基于相对步宽的两足步行结构的机械能耗研究

在对高邮鸭、珍珠鸡、人的观测和对非洲鸵鸟、仙鹤、皇企鹅的生物学调研基础上,分析不同的两足步行机构的几何特点与其步宽大小的关系,发现特定动物的步宽与腿长的比值是一个常数,不随速度而发生变化,据此定义相对步宽。从步宽与腿长的综合角度出发,建立动力学模型,计算出机械能损耗与相对步宽之间的关系,不同动物步行的实际能耗数据证明该结论正确。该结论为步行机器人下肢的结构设计和步态规划提供了重要的理论依据和设计思想。     

基于过程ZMP的双足步行机器椅步态规划

解决了多关节双足步行机器椅行走步态过程稳定性评价与其开环多连杆执行机构的多变量泛函问题.从构造多关节双足步行机器椅行走姿态和过程ZMP(Zero Moment Point,零力矩点)评价考虑,提出了基于优化方法的多关节双足步行机器椅行走步态的离散化模型和方法,实现了基于过程稳定性评价的双足步行机器椅的开环多连杆执行机构行走步态的合理规划.文中提出的离散化模型对求解开环连杆机构的多变量泛函规划问题具有重要的参考价值.     

基于多模态步行意图识别的助行机器人柔顺控制

在辅助行走或步行康复训练过程中,助行机器人在紧密跟随人体步态的基础上,准确识别异常行为是人机交互的重要研究内容。为此,提出一种兼具通用性、鲁棒性与便捷性的非接触式多模态步行意图识别方法,能够准确识别多种步态并柔顺地控制机器人运行。首先,分析了步行辅助机器人和步行康复训练机器人的结构、功能与运动学模型,建立了内嵌式机载步态信息检测系统,从而准确描述步态变化规律;其次,为有效解决标志点丢失问题,提出了一种新型的扩展集员滤波算法来精确估计膝关节角度;最后,通过引入用户步态信息,建立了一种基于步态补偿的柔性控制方法并进行了实验研究。实验表明,提出的算法能够在有效克服标记点丢失的情况下,准确识别交互过程中的正常步态,并柔顺地控制机器人运动,同时对跌倒和拖拽步态进行有效识别,识别率分别达到91.3%和89.3%。该非接触式步态意图识别方法可以应用于具有类似结构的助行器及其日常助行与康复训练场景。